The invention generally relates to testing equipment for digital data communications systems, and more particularly to performance testing equipment which generates standardized traffic patterns in order to test Asynchronous Transfer Mode (ATM) communication devices.
Performance testing of ATM data communication devices such as network nodes or switches is becoming more important as the ATM data communication technology matures. This is because the majority of ATM equipment providers implement standard protocols which have more or less equivalent functionality. Thus, the distinguishing factor between similar ATM communication devices is their performance under known, real world, conditions. Accordingly, the performance of an ATM device is one factor upon which customers base their purchasing decisions. The desire for performance testing requirements can be seen in the standards setting bodies and industry associations such as the International Telecommunications Union (ITU), the Internet Engineering Task Force (IETF) and the ATM Forum, where numerous performance testing specifications are currently in the process of being drafted.
Equipment for testing performance of ATM communications devices already exist. For example, the Interwatch 95000 by GN Nettest can generate ATM Adaptation Layer test frames.
However, effective performance testing requires the use of standardized traffic patterns, called reference load models (RLMs), for evaluating a system under test. The standardized traffic patterns are generated on the input ports of the device or system under test to see how it behaves under certain conditions. These standardized traffic patterns must be reproducible so that similar devices or systems from competing manufacturers can be compared under the same conditions.
Moreover, a good ATM reference load model generator does not exist at the xe2x80x9cframe levelxe2x80x9d, i.e., the level at which user information is packaged or presented prior to being converted into an ATM cell stream. Current ATM test generators are simple cell based generators that generate frames of a constant size. This type of frame traffic does not model real world traffic patterns.
Accordingly, there is a need for ATM test generators that can generate dynamic and well defined frame traffic patterns. Such a test generator should be able to generate a wide variety of frame traffic patterns, including frames of various size and spacing, using a set of standardized parameters which allow for reproducibility. With this type of generator, realistic traffic patterns can be modelled, and realistic and effective performance of ATM devices or systems can be achieved.
Broadly speaking, the invention provides a reference load model generator, comprising interface means for specifying a frame size (FS), an inter-frame gap (IFG) and an inter-cell gap (ICG) for modelling one or more frame sources. A frame source generator generates respective source cell streams, each according to the specified FS, IFG and ICG of the corresponding modelled frame source. A multiplexer receives the source cell streams and generates a single output stream.
In a preferred embodiment of the present invention, the interface means further specifies an arbitration scheme utilized by the multiplexing means in generating the single output stream.
Another broad aspect of the invention relates to a method for generating an ATM cell stream, comprising the steps of: (a) specifying a frame size (FS), an inter-frame gap (IFG) and an inter-cell gap (ICG) so as to model one or more frame sources; (b) generating respective source cell streams, each having the specified FS, IFG and ICG of the corresponding modelled frame source; and (c) generating a single output stream by multiplexing the source cell streams.
In a preferred embodiment of this aspect of the invention, the method further comprises the steps of specifying a multiplexer arbitration scheme, and multiplexing the source cell in accordance with the scheme so as to generate the single output stream.
In the preferred embodiment, the source cell streams are ATM cell streams defined at the frame level. In the preferred embodiment, the frame level is correlated to the common part convergence sublayer (CPCS) of the ATM adaption layer (AAL), such that the preferred source cell streams carry CPCS protocol data units (PDUs), for example, AAL 3/4 and 5 PDUs. The frame level may alternatively be correlated to other layers of the ATM protocol stack, whereby the source cell streams carry, for example, FR-SSCS PDUs.
The frame size is the length of a frame (i.e., at the frame level) in terms of the number of cells per frame. The inter-frame gap is the number of idle cells in the stream between successive frames. The inter-cell gap is the number of idle cells between successive non-idle cells in a given frame. The interface means allows these parameters to assume non-constant values, e.g., the FS may be specified by a random number generating function having a uniform distribution over a pre-selected range. The frame generator produces source ATM cell streams accordingly.
Collectively, the FS, IFG and ICG frame source parameters provide a minimal set of parameters in terms of the structure of a cell stream to adequately characterize traffic patterns at the frame level. As such, the traffic pattern of a standardized ATM cell stream may be characterized, and hence reproduced by various test generators, by specifying a number of input frame sources, the FS, IFG and ICG parameters for each such frame source, and a multiplexer arbitration scheme. This further allows reproduction of experiments by different test laboratories which is an important requirement in connection with performance testing.
In the preferred embodiment, the transmission rates of each of the source ATM cell streams and the output ATM cell stream may be also specified, if desired. The specification of the transmission rates further characterizes the traffic patterns of the output cell stream since, other things being equal, the presentation of cells to the multiplexer will vary depending on the transmission rates of the corresponding source cell streams.